The traditional Public Switched Telephone Network (PSTN) operated in the current fashion is encountering increasing difficulties in satisfying emerging communications requirements having diverse characteristics. As a partial result there has been a trend to proliferation of private and semi-commercial networks customized to carry specific types of traffic. While these specialized networks are effective for their limited purposes the result has been the creation of a maze of disparate networks resembling the patchwork system which existed in the early 20th Century before the public networks were interconnected. This proliferation of specialized networks and private solutions serves to make communication more compartmentalized and to duplicate facilities already in existence. This failure to efficiently utilize available infrastructure apparently is due in part to a lack of understanding and appreciation of the current availability and capability of the Advanced Intelligent Network (AIN) in its present stage of development and installation.
In traditional PSTN practice telephony features, such as Call Forwarding, have been based on feature logic and data contained within the Stored Program Control (SPC) Switches in the network. The feature logic is contained within the software programs provided by the switch vendors and the introduction of new features has required new software programs from the switch vendors. Having the feature data contained in the switches has impacted the administration of the data for customers served by several switches and the Telco has been forced to coordinate feature data administration across multiple systems to ensure correct and consistent feature operation.
The concept of the Advanced Intelligent Network (AIN) has been to provide services based on feature logic and data located at a centralized node in the network rather than in each individual switching system node. Appropriately equipped switches in the network, known as Services Switching Points (SSP) communicate with a centralized node, known as a Service Control Point (SCP) database, and together, they provide various AIN services. The Service Management System (SMS) is an operations system used to administer data in the SCP and to provide other operations, administration and maintenance functions for the AIN.
The SSP knows which calls require AIN service based on characteristics of the call, such as the line from which it originated or the digits which were dialed. The process of identifying calls that require AIN processing is known as triggering, since a particular characteristic of the call triggers the switch into providing AIN treatment. Once a trigger occurs a query message is sent to the SCP asking for instructions. Based on information contained in the query message the SCP determines which service is being requested and provides appropriate information such as routing and billing instructions. The SSP then executes this routing and these instructions to complete the call.
Only the SCP knows which service is being performed on a particular call. The SSP simply knows how to identify calls that require AIN processing, and how to execute instructions provided by the SCP. This architecture provides the first stage of realizing AIN capabilities and is predicated on providing SSP capabilities for SPC switches such as the 5ESS and 1AESS and the like switches.
Referring to FIG. 1 there is shown in schematic block diagram form a depiction of the components of the AIN within a region. In this figure the Central Offices (CO) are labeled as SSP 11, 13, 15, 17, 215 and 217. The SSPs 11 and 13 connect to a first local area Signal Transfer Point (STP) 23, and the SSPs 15 and 17 connect to a second local STP 25. The connections to the STPs are for signaling purposes using common channel signaling 7 (CCS7 or SS7). As is understood by those skilled in the art, common channel signaling separates the signaling path from the path used for voice transmission. The Common Channel Signaling Network (CCSN) provides signaling instructions needed by the voice network to set up, route and terminate calls. Specialized databases connected to the CCSN permit the signaling network to transport the specialized routing or terminating instructions which the databases contain. A typical CCSN network is illustrated in FIG. 2.
The SSPs 11 and 13 connect to a first local area STP 23 and the SSPs 15 and 17 connect to a second local area STP 25. As indicated by the black dots below STPs 23 and 25, each local area STP can connect to a large number of the SSPs. Although not shown in FIG. 1 the central offices or SSPs are interconnected to each other by trunk circuits for carrying telephone services.
The local area STPs 23 and 25 and any number of such local area STPs shown as black dots between STPs 23 and 25 communicate with a state or regional STP 31. The state or regional STP 31 in turn provides a communications link with the ISCP 40 (Integrated Service Control Point). The STP hierarchy can be expanded or contracted to as many levels as needed to serve any size area and to service any number of stations and central office switches. The links 23 and 25 between the CO/SSPs and local area STPs are dedicated CCIS links which are typically SS7 type inter-office data communications channels. The local area STPs are in turn connected to each other and to the regional STP 31 via a packet switched network. The regional STP 31 also communicates with ISCP 40 via a packet switched network.
As shown in FIG. 1, the ISCP 40 is an integrated system. Among other system components, the ISCP 40 includes a Service Management System (SMS) 41, a Data and Reporting System (DRS) 45 and the actual database or Service Control Point (SCP) 43. The ISCP also typically includes a terminal sub-system referred to as a Service Creation Environment or SCE 45 for programming the database in the SCP 43 for the services subscribed to by each individual business customer.
Each central office switching system normally responds to a service request on a local communication line connected thereto to selectively connect the requesting line to another selected local communication line. The connection can be made locally through only the connected central office switching system. For example, for a call from station A to station B the SSP/CO 11 provides the call connection without any connection to another central office. When the called line connects to a distant station, for example, when station A calls station C, the connection is made through the connected central office switching system SSP 11 and at least one other central office switching system SSP 13 through the telephone trunks interconnection of the two COs.
The basic operation of the CCSN network is as follows: Based on some characteristic of the call (for example, the line from which the call originated, or the access code that was dialed), the SSP determines that the call requires AIN processing. This process is known as triggering, and it results in the SSP suspending call processing, sending a query message to the SCP and waiting for instructions. The query message is sent to the SCP via a Signaling Transfer Point (STP).
Based on information in the query message, and on the current status of the network, the STP determines which SCP should process the query, and it forwards the query message to that SCP. When the SCP receives the query message it first determines which service is being requested since an SCP typically contains logic and data for many different services and customers. Once this is done, the SCP begins processing the service logic.
The SCP service logic, which is typically constructed directly by the Telco, uses various criteria to determine how to handle the call. Examples of these criteria are the calling number, the dialed number, the day of week, and the time of day. Once the SCP has determined how to process the call, it sends a message containing instructions back to the SSP. In the simplest case, these instructions would be sufficient to route the call, and the SCPs function for that call would be complete. However, for more complex services, several messages might be sent back and forth between the SCP and the SSP until the SCP has sufficient information to provide final instructions for the call.
Of the three types of offices shown in FIG. 1, only the SSP can communicate with the SCP. Thus conventional POTS end offices (EOs) must route AIN calls to the SSP where full AIN processing can occur.